A screw connecting terminal of this generic type has a clamping part, which is essentially in the form of a frame with longitudinal, narrow and broad faces, a clamping screw which is held in a threaded opening in the clamping part, and a busbar which passes through the interior of the frame-like clamping part and is arranged such that it can move with respect to the clamping part, and whose broad face in the installed state is oriented parallel to the broad face of the clamping part, with the clamping part being movable in its longitudinal direction relative to the busbar by rotation of the clamping screw, such that a connecting conductor can be clamped firmly between the side of the busbar which faces away from the clamping screw and the broad face of the clamping part which faces away from the clamping screw.
Screw connecting terminals of this generic type are also known as strain-relief clamps. DE 40 13 225 B4 and DE 101 55 924 A1 disclose examples of embodiments of generic strain-relief clamps. These are normally used in service switching devices, for example in circuit breakers or residual current devices, in order to connect connecting conductors, to the service switching device, irrespective of whether these connecting conductors are stripped cable ends of flexible wiring cables or fixed contact lugs of busbar arrangements. As is known, service switching devices are used to monitor and to connect and disconnect the current flow on a current path which passes through the interior of the appliance from a connecting terminal on the input side to one on the output side. For this purpose, the screw connecting terminals are fitted in the interior of the service switching device housing, in a terminal accommodation area which is generally accommodated close to the narrow face of a service switching device such as this.
The busbar is generally mounted in a fixed position in the interior of the housing. Internal connecting conductors are fitted to its free end facing the interior of the appliance and continue the current path between the connecting terminals on the input and output sides, with the current path also being passed by further functional assemblies or components in the housing interior, for example via a contact point, and possibly via a thermal or magnetic release.
Since the busbar is mounted in a fixed position, the clamping part moves relative to the busbar during operation of the clamping screw. During production of a service switching device, it is often necessary to carry out so-called thermal adjustment of the thermal release at the end of the manufacturing process. For this purpose, test probes in a test apparatus make contact with a specific contract pressure with the busbars of the connecting terminals on the input and output sides, during which process it is possible for the busbar to be pushed from its fixed position into the interior of the housing by the contact pressure of the test probe, thus rendering the appliance no longer useable.